Ken and Barbara have two children, aged three and six. At the end of every six months for the next 12_1 years, they wish to contribute equal amounts to a Registered Education 2 Savings Plan (RESP). Six months after the last RESP contribution, the first of 12 semiannual withdrawals of $5000 will be made. If the RESP earns 8.5% compounded semiannually, what must be the size of their regular RESP contributions?